1. Field of the Invention
This invention relates to an electronic still camera for recording stationary images.
2. Related Background Art
FIG. 1 of the accompanying drawings is a block diagram showing the construction of an electronic still camera according to the prior art using a contour enhancement circuit.
In FIG. 1, an object to be photographed, not shown, has its quantity of light adjusted by a stop member 2 and is imaged on the image pickup surface of an image pickup element 3 by an optical lens 1, and the light signal of the image is converted into an electrical signal. The image pickup element 3 comprises various solid state image pickup elements such as a CCD (charge coupled device), an MOS device and an SIT. The output of the image pickup element 3 is connected to a sample hold circuit 5. A drive pulse generator 4 generates a pulse for driving the image pickup element 3 to the image pickup element 3, and generates a sample pulse for sampling and holding to the sample hold circuit 5. The sample hold circuit 5 samples and holds the output signal from the image pickup element 3 at the timing of the sampling pulse from the drive pulse generator 4, and outputs an analog image signal to an amplifier circuit 6. The image signal amplified by the amplifier circuit 6 is then input to a contour enhancement circuit 7, in which the process of enhancing the change of the image signal is carried out. The output signal of the contour enhancement circuit 7 is input to a level adjustment circuit 8 for adjusting the white clip level and the set up level, and the output signal of the level adjustment circuit 8 is input to a recording portion 9.
The reference numeral 13 designates a light metering element for metering the quantity of light of the object to be photographed before photographing. The light metering element 13 is designed such that the image of the object to be photographed is formed thereon by a condensing lens 12. The image formed on the light metering element 13 is converted into an electrical signal by the photoelectric converting function of the light metering element 13 and is output to an amplifier 15. The electrical signal amplified by the amplifier 15 and logarithmically compressed is converted into a digital signal by an A/D converter 16 and is input to a central calculation processing portion 10. Also, a stroboscopic lamp 11 which is a light emitting device is provided to momentarily illuminate the object to be photographed when it is dark.
A release button 18 is a switch for the user to make the camera ready to photograph, and is operatively associated with contacts 17a, 17b and 17c. The contacts 17a, 17b and 17c are connected to the central calculation processing portion 10. When the release button 18 is depressed lightly, the contacts 17a and 17b are closed and the central calculation processing portion 10 performs a photographing preparation operation such as light metering. When the release button 18 is further depressed and the contacts 17b and 17c are closed, the central calculation processing portion 10 performs photographing operations such as the charge accumulation of the image pickup element 3 and the recording of the image signal.
The central calculation processing portion 10 connected to the recording portion 9 and the drive pulse generator 4 controls the operation of the present apparatus, determines the size of the aperture diameter of the stop member 2 and the charge accumulation time in the image pickup element 3 from the output signal of the light metering element 13 converted by the amplifier 15 and the A/D converter 16, controls the light emission of the stroboscopic lamp 11, controls the generation of pulse to the drive pulse generator 4, and causes the recording portion 9 to record the output signal from the level adjustment circuit 8.
In the above-described construction, when in photographing, the release button 18 is depressed lightly by the user and the contacts 17a and 17b are closed, the quantity of light of the object to be photographed, not shown, is metered by the light metering element 13, and the size of the aperture diameter of the stop member 2 and the charge accumulation time in the image pickup element 3 are determined. When the central calculation processing portion 10 judges that the object to be photographed is dark and sufficient exposure will not be obtained, the preparation for the light emission of the stroboscopic lamp 11 is effected. When the release button is then depressed deeply, the contacts 17b and 17c are closed, and the light from the object to be photographed, not shown, enters the image pickup element 3 through the optical lens 1 and the stop member 2, and as previously described, the image signal provided by the image pickup element 3 and the sample hold circuit 5 is input to the amplifier circuit 6. The image signal is electrically amplified in conformity with the predetermined amplification degree of the amplifier circuit 6 and subsequently, has its white clip level and set up level adjusted by the level adjustment circuit 8, and is recorded by the recording portion 9.
The prior art as described above has suffered from the following problems.
When in general photographing, the difference in quantity of light between the light portion and the dark portion of an object to be photographed is small, for example, as in a scene during cloudy weather, if contour enhancement is done at the standard contour enhancement degree in the contour enhancement circuit, the contrast of the image will be too weak and modulation will become null and therefore, a visually good image will not be obtained. Also, when the difference in quantity of light between the light portion and the dark portion of an object to be photographed is great, such as when a figure is photographed during fine weather or when a stroboscopic lamp is used, if contour enhancement is done at the standard contour enhancement degree in the contour enhancement circuit, the contrast of the image will be too strong and modulation will become too strong and again, a visually good image will not be obtained.
As described above, in the prior art, the setting of the contour enhancement degree is fixed in the contour enhancement circuit and contour enhancement is done always at the same enhancement degree, and this has led to the problem that contour enhancement matching an object to be photographed is not done and depending on the situation of the object to be photographed, a visually good image of good contrast is not always obtained.
FIG. 2 of the accompanying drawings is a block diagram showing the construction of an electronic still camera according to the prior art using a gray scale modification circuit.
In FIG. 2, optical members and circuits given reference numerals identical to those in FIG. 1 are identical to those in FIG. 1 and therefore need not be described.
The output signal of the contour enhancement circuit 7 is input to a gray scale modification circuit 19, in which gamma correction is effected so that the image may assume the standard gray scale. The output signal of the gray scale modification circuit 19 is input to the level adjustment circuit 8 for adjusting the white clip level and the set up level, and the output signal of the level adjustment circuit 8 is input to the recording portion 9.
The image signal is electrically amplified in conformity with the predetermined amplification degree of the amplifier circuit 6, and has predetermined contour enhancement applied thereto by the contour enhancement circuit 7. Subsequently, modification of the gray scale is effected by gamma correction at the standard .gamma. value preset in the gray scale modification circuit 19, and then the image signal has its white clip level and set up level adjusted by the level adjustment circuit 8 and is recorded in the recording portion 9.
The prior art as described above has suffered from the following problems.
When in general photographing, the difference in quantity of light between the light portion and the dark portion of an object to be photographed is small, for example, as in a scene during cloudy weather, if gray scale modification by gamma correction at the standard .gamma. value is effected in the gray scale modification circuit, the contrast will be weak and therefore, a visually good image will not be obtained. Also, when the difference in quantity of light between the light portion and the dark portion of an object to be photographed is great, such as when a figure is photographed during fine weather or when a stroboscopic lamp is used, if gray scale modification by gamma correction at the standard .gamma. value is effected in the gray scale modification circuit, the contrast will be strong and therefore, a visually good image will not be obtained.
As described above, in the prior art, gray scale modification by gamma correction always at the standard .gamma. value is effected in the gray scale modification circuit and therefore, the gray scale modification characteristic is fixed and gray scale modification matching the object to be photographed is not done, and this has led to the problem that depending on the situation of the object to be photographed, a visually good image cannot always be obtained.